CHICAGO—Merck’s Keytruda already boasts a standalone approval for lung cancer patients who haven't been treated before, so long as their tumors bear high levels of the PD-L1 biomarker. But it could soon reach beyond that group, thanks to data unveiled Sunday.

At the American Society of Clinical Oncology annual meeting, the New Jersey drugmaker rolled out results showing the drug helped patients live longer, regardless of PD-L1 level.

Keytruda monotherapy cut the risk of death by 19%, compared with chemo, in all patients who tested positive for the PD-L1 biomarker. The trial, Keynote-042, covered patients with both the squamous and non-squamous forms of non-small cell lung cancer.

Among patients with high PD-L1 levels, the drug performed even better. In those with levels of 20% or higher, Keytruda pared down the risk of death by 23%, and in those at 50% or higher, it cut the risk of death by 31%.

As analysts pointed out, though, higher numbers in the PD-L1-high group left room for improvement in PD-L1-low patients. "The benefit was clearly driven by patients with greater levels of PD-L1 expression," Credit Suisse's Vamil Divan wrote to clients. He added that while the new data will likely score Merck an expanded indication, "the fact that KN-042 was not overwhelmingly positive in patients with PD-L1 levels of 1-49% leaves that population potentially more available to better combination therapy approaches in the future."

Merck, for its part, wasn’t surprised to see Keytruda post benefits across the PD-L1 board, said Roy Baynes, Merck SVP and head of global clinical development. He pointed out that Keytruda has recorded a survival benefit in each of five randomized controlled lung cancer trials. The company has “a lot of confidence in the molecule,” he said.

The question now, though, is how doctors will use the data. Merck’s Keytruda-chemo combo has already put up a stellar phase 3 showing in previously untreated patients, including cutting the risk of death by 51%.

“I think all things being equal, we would say that chemo combo offers a very, very good probability of a good outcome. If patients have comorbidities or reasons for which either the patient or the physician might be concerned that chemo may not be the best option, and if the patient is PD-L1 positive, it’s at least our position that monotherapy offers a reasonable option,” Baynes said.

After some major victories recently, Keytruda is in prime position to run the all-important first-line lung cancer market. Also Sunday at ASCO, the company unveiled positive chemo-combo data in squamous first-line lung cancer, filling a hole in its patient population. Previously its data had focused mostly on patients with non-squamous disease.

“There are options for pretty much all patients in frontline,” Baynes said. With “really favorable data for a positive outcome,” Keytruda can now address “pretty much all of the lung cancer patients” other than those with specific mutations.